Semester

Spring

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Wildlife and Fisheries Resources

Committee Chair

Kyle J. Hartman.

Abstract

The Ugashik Lakes in southwest Alaska are a large, remote, thereimictic system that does not thermally stratify during the ice-free season. Little research has been done on the resident species of this system and others similar to it. However, with such little baseline information management agencies are still responsible for management of these lakes. In order to provide baseline data on the Ugashik Lakes resident species, hydroacoustic (2001-06) and gillnet (2004-06) surveys were performed.;Chapter 2 uses specific data gathered from the hydroacoustic unit to produce a target strength (TS) and length relationship for salmonids found in the Ugashik Lakes. The equation produced from this experiment is of the standard format using a slope of 20: TS = 20 · log10(L cm) -- 78.53 (R2 = 0.49). This relationship differs markedly from the commonly used equations of Love and Foote.;In Chapter 3 using the hydroacoustic and gillnet datasets I determined fish density and abundance estimates for each resident species in the Ugashik Lakes. These estimates showed large annual variances. I discuss the possible causes of these large variance values from the perspective of sampling and systematic error. The large variances prevent meaningful statistical comparisons. However, these estimates may still prove useful in monitoring fish populations through time series analysis.;Along with fish density data, hydroacoustics collects large amounts of data on the spatial distribution of fish and bathymetry of the lakes being sampled. Chapter 4 addresses the use of GIS software to create detailed maps showing the bathymetry and distribution of fish density in The Ugashik Lakes. Natural neighbor interpolation was used to fill in data gaps between hydroacoustic survey transects.;This will aid in the visual presentation of fisheries data. From the hydroacoustic and gillnet surveys I was able to develop an annual sampling strategy as an appendix that a fisheries management agency can implement. I present both echo integration and echo counting procedures used for hydroacoustics data. Within each of these procedures I present various statistical analyses and their strengths and weaknesses that can be used to determine density and abundance estimates. Apportioning species by density estimates was determined using gillnet catch percentages. In addition, I discuss the most efficient means of collecting both hydroacoustic and gillnet data to suit the Ugashik Lakes and other similar lake systems.

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